This invention relates to inspection probes for measuring the dimensions of workpieces in numerically controlled machine tools. Examples of prior art inspection probes of this type are found in U.S. Pat. Nos. 3,571,934; 3,520,063; and 3,250,012.
As described in the above-noted U.S. patents, the prior inspection probes contain a probe member which is movably mounted in a housing and is coupled to a transducer which produces an output signal indicating the amount of deflection of the probe member from its reference position. The housing is mounted in the spindle of a machine tool containing a workpiece whose dimensions are to be measured. The spindle is then moved by the numerical controls to a predetermined reference position in which the probe member makes contact with the workpiece. The deflection of the probe member when the spindle is in its reference position is used to indicate the corresponding error of the workpiece.
With these prior art probes, the accuracy of the dimensional measurement is limited by the accuracy of the probe deflection measuring means rather than by the accuracy of the numerical control positioning means since the latter is only used to bring the measurement probe to a reference position; the distance from the reference position to the workpiece being indicated by the deflection of the probe member.